A previous study also demonstrated that the overexpression of miR-4521 can reduce the in vitro migration and invasion ability of ccRCC cells 786-O and ACHN through the TIMP-1/MMP2/MMP9 pathway, and promote their apoptosis through the MDM2/p53/Bcl2/Bax pathway to reduce its proliferation [21]. This evidence concerns the gene MMP9 and nonpapillary renal cell carcinoma.